1. Field of the Invention
The present invention relates to solid-state imaging devices which read an image by using solid-state image sensors, and relates to semiconductor packaging techniques which are applicable to the production of solid-state imaging devices used in copiers, image scanners, facsimiles, digital cameras, video cameras or the like.
2. Description of the Related Art
Conventionally, the dominant method of production of solid-state imaging device is to produce a package that contains a solid-state image sensor, such as CCD (charge-coupled device), the package typically made of a ceramic insulating substrate.
FIG. 6 shows a conventional solid-state imaging device.
As shown in FIG. 6, the conventional solid-state imaging device includes a ceramic package 802 having a plurality of external terminals 801. The package 802 contains a solid-state image sensor 803, the package 802 being made of a ceramic insulating substrate. Hereinafter, the package itself (or the ceramic insulating substrate) will be referred to as the ceramic package. The external terminals 801 are provided for the solid-state imaging device to output an electrical signal to an external device via the external terminals 801.
The ceramic package 802 includes a recessed portion 802a at its upper surface, and the solid-state image sensor 803 is mounted on the recessed portion 802a of the ceramic package 802. The solid-state image sensor 803 has an effective light-receiving region, and the solid-state image sensor 803 is placed with this light-receiving region in a face-up condition.
In the recessed portion 802a of the ceramic package 802, electrodes 804, which are connected to the external terminals 801 in the ceramic package, are provided at internal peripheral locations of the recessed portion 802a. The solid-state image sensor 803 also includes electrodes at peripheral locations of the upper surface of the image sensor. By performing a wire bonding, the electrodes 804 of the ceramic package 802 are electrically connected to the electrodes of the image sensor 803 by wires 805. The wires 805 are made of, for example, aluminum (Al) or gold (Au). Further, in order to protect the solid-state image sensor 803, a silica glass 806 is attached to the top of the recessed portion 802a of the ceramic package 802 as a sealing cover for protecting the image sensor 803 from mechanical damage and environmental influences.
During an operation of the imaging device of FIG. 6, incident light 807, which is derived from an object to be imaged, passes through the silica glass 806 on the top of the recessed portion 802 of the ceramic package 802, and reaches the solid-state image sensor 803. The light-receiving region of the image sensor 803 for receiving the incident light 807 is formed with a large number of photodiodes (not shown). The number of photodiodes in one solid-state image sensor varies depending on the type of the image sensor, and the number of photodiodes in the image sensor 803 is typically in a range from 20,000 to 40,000. The image sensor 803 generates an electrical signal through the optoelectronic conversion of the received light, and the signal, output by the image sensor 803, is processed as image data in an image reading unit (not shown).
In the case of a recent solid-state image sensor in which a larger number of tiny photodiodes are more densely provided, a micro-lens of a resin material is additionally formed on the light-receiving region of the image sensor for the purpose of increasing the sensitivity of the photodiodes to receiving light. In such a case, the incident light 807 passes through the silica glass 806, and it is converted by the micro-lens into a convergent light, so that the convergent light reaches the light-receiving region of the solid-state image sensor 803. Similarly, the image sensor 803 generates an electrical signal through the optoelectronic conversion of the received light, and the signal, output by the image sensor 803, is processed as image data in an image reading unit.
FIG. 7A, FIG. 7B and FIG. 7C show a conventional method of production of the solid-state imaging device shown in FIG. 6.
In a first step of the production method of the solid-state imaging device, the die bonding process as shown in FIG. 7A is performed. The solid-state image sensor 803 is placed into the recessed portion 802a of the ceramic package 802 with the light-receiving region of the image sensor 803 in a face-up condition. The ceramic package 802 is provided with the external terminals 801. The image sensor 803 is bonded to the ceramic package 802 by using a die bonding machine. The die bonding process to bond the image sensor 803 onto the ceramic package 802 is performed by using a conductive adhesive agent, such as a thermosetting silver paste. The curing of the conductive adhesive agent, which is provided between the image sensor 803 and the ceramic package 802, is attained by heating it to about 150 deg. C.
In a second step, the interconnecting process as shown in FIG. 7B is performed after the end of the die bonding process. The electrodes 804 at the internal peripheral locations of the recessed portion 802a are electrically connected to the electrodes at the peripheral locations of the upper surface of the image sensor 803 by the wires 805 of aluminum or gold. The interconnecting process to interconnect these electrodes is performed by using a wire bonding machine. The electrodes 804 are respectively connected to the external terminals 801 in the ceramic package 802.
In a third step, the encapsulation process as shown in FIG. 7C is performed after the end of the interconnecting process. The silica glass 806 is attached to the top of the recessed portion 802a of the ceramic package 802 as a sealing cover that protects the image sensor 803 from mechanical damage and environmental influences. The conventional imaging device is thus produced. When the silica glass 806 is attached to the ceramic package 802 as the sealing cover, it is necessary to maintain the internal space between the silica glass 806 and the ceramic package 802 in a vacuum condition before and after the encapsulation process. The silica glass 806 must be bonded to the ceramic package 802 under a vacuum condition, and the bonding process to bond the silica glass 806 to the ceramic package 802 is performed by using a thermosetting adhesive agent.
In the above-described solid-state imaging device, the electrical connections of the package electrodes 804 and the image sensor electrodes are established by the wires 805. In order to arrange the wires 805 at the peripheral locations of the upper surface of the image sensor 803 where the electrodes are provided, the ceramic package 802 requires a relatively wide area to form the electrodes 804 at the internal peripheral locations of the recessed portion 802a. Further, the internal space between the image sensor 803 and the silica glass 806 must be wide enough to accommodate the looped portions of the wires 805 therein. Therefore, it is difficult to develop a small-size, light-weight imaging device based on the structure of the conventional imaging device.
An object of the present invention is to provide an improved solid-state imaging device in which the above-described problems are eliminated.
Another object of the present invention is to provide a solid-state imaging device which not only provides small-size, lightweight features but also provides reliable protection of the imaging performance against mechanical damage and environmental influences.
Another object of the present invention is to provide a method of production of a solid-state imaging device which not only provides small-size, light-weight features but also provides reliable protection of the imaging performance against mechanical damage and environmental influences.
The above-mentioned objects of the present invention are achieved by a solid-state imaging device comprising: a solid-state image sensor which has an effective light-receiving region on a circuit formation surface provided in a face-down condition; a transparent substrate which has a conductor pattern provided thereon to confront the circuit formation surface of the image sensor; a transparent adhesive agent which is provided between the image sensor and the substrate and formed into a thin layer, the adhesive agent covering the light-receiving region of the image sensor; and a plurality of bumps which are provided on one of the image sensor and the substrate to interconnect the image sensor and the conductor pattern of the substrate.
The above-mentioned objects of the present invention are achieved by a method of production of a solid-state imaging device comprising the steps of: providing a solid-state image sensor having an effective light-receiving region on a circuit formation surface provided in a face-down condition; providing a transparent substrate having a conductor pattern provided thereon to confront the circuit formation surface of the image sensor; providing a plurality of bumps on one of the image sensor and the substrate; supplying a predetermined amount of a transparent adhesive agent between the image sensor and the substrate, the amount of the adhesive agent being large enough to fully cover the light-receiving region of the image sensor; moving the image sensor closer to the substrate until a predetermined distance between the image sensor and the substrate is reached, so that the bumps interconnect the image sensor and the conductor pattern of the substrate; forming the adhesive agent between the image sensor and the substrate into a thin layer, the thin layer of the adhesive agent covering the light-receiving region of the image sensor; and curing the adhesive agent.
In the solid-state imaging device and the production method according to the present invention, the circuit formation surface of the image sensor having the effective light-receiving region thereon is provided in a face-down condition, and the conductor pattern of the substrate is provided to confront the circuit formation surface of the image sensor. The transparent adhesive agent is provided between the image sensor and the substrate and formed into a thin layer, the adhesive agent covering the light-receiving region of the image sensor. Therefore, the solid-state imaging device and the production method of the present invention not only provide small-size, light-weight features but also provides reliable protection of the imaging performance against mechanical damage and environmental influences. Further, the production method of the present invention is useful and effective in easy and low-cost production of the solid-state imaging device that provides small-size, light-weight features as well as reliable protection of the imaging performance against mechanical damage and environmental influences.